According to studies developed by the Ministry of Mines and Energy of Colombia, due to high prices of liquid fuels for external factors, Natural Gas Vehicle (NGV) emerged as an alternative, which has led to different actions by the Government and Entities such as Ecopetrol and Eicogas, among others, that seek to encourage the number of conversions to natural gas vehicle as a strategy to massify its use and replace the use of other more expensive fuels such as gasoline, Diesel Oil, among others.
At present, Natural Gas Vehicle (NGV) has gained greater relevance regarding the increase of costs of fuels derived from petroleum, as, through the use of natural gas, it produces less harmful substances to the environment, provides a longer shelf life of the engine's oil, the operation of natural gas engines is smoother compared to diesel and therefore less noisy, among other advantages.
Given the current demand for natural gas-fueled engines, as they produce much less CO2 pollution compared to diesel engines, there have been proposed different alternative engines allowing their operation by varying the input fuel. This led, not only in Colombia, but also worldwide, to the conversion of diesel-type engines to natural gas, a process known as conversion (there can be found extensive information on how to conducted it). One of the requirements of this process consists in the reduction of the compression ratio to allow an optimal combustion with the new fuel.
The reduction of the compression ratio of the engine is widely used worldwide by engineers of high performance engines, information of which is documented in forums and websites specialized in the field. However, there is no evidence that the reduction of the compression ratio can be made by a process that reversibly modifies the engine head. Similarly, and despite the evidences in the processes published in documents that are made to reduce the compression ratio, there is no single reference mentioning that said process can be carried out by metallization of the cylinder head and less that this process can be carried out for the conversion of diesel engines to natural gas.
Werner Funk et al. in the U.S. Pat. No. 7,019,626 B1 patent discloses the design of engines that can run on different types of fuels, whether diesel or a second fuel such as natural gas, propane, or hydrogen. However, the conversion of a multi-fuel engine requires modification of the engine including an indicator that indicates how much second fuel is being combusted relative to the diesel or gasoline, as well as an oil control unit of the fuel pump and a control unit for the metering of the second fuel. While this document relates to an engine that can be used on two different fuels, it does not provide the possibility to reuse the engine exclusively for diesel fuel since it requires internal drastic structural changes on said engine.
Likewise, a process for the conversion of a diesel engine to natural gas has been disclosed in US20030089346 A1, where inserting a spark plug into the fuel injection system for the use of natural gas is proposed, which also requires the installation of a throttle body in the diesel engine, the installation of an accelerator body adapter between an accelerator body and an intake manifold of said diesel engine and modification of the piston so that the compression ratio reduces and improves efficiency when the fuel is natural gas. Although this invention also seeks to reduce the compression ratio by modifying the pistons by removing part of the material therein, it has to be taken into account that multiple internal modifications of the engine for its transformation will obviously lead to high production and assembly costs.
The above process is the best known and used for the conversion of engines for which various modifications are required, such as adapting an acceleration body, mounting gas and ignition supply systems and reducing the compression ratio. However, a clear disadvantage of this process is the disassembly and permanent modification of the piston, so that the installation times are increased and it is not a reversible process. In fact, this change in the volume of the piston causes it to weaken and when the engine is need to run again with diesel, new pistons are required. Despite the evidences in the processes that are carried out to reduce the compression ratio, there is no evidence that this process is made by metallization of the cylinder head and less that this process can be carried out for the conversion of engines.
Other documents relating to the invention are directly related with a spatter plate which is installed between the cylinder head and the cylinder block so that the compression in the diesel engine can be reduced, a spark source can be provided and the compression ratio can be reduced. A combustion chamber volume is generated by including such spatter plate, which reduces the compression ratio required to use natural gas as fuel. However, said spatter plate provides a spark source, which makes it complex and expensive, and is a thin element that is likely to fail because it has to support high pressures and temperatures that occur in the combustion chamber.
Likewise, some companies in different parts of Latin America have sought the conversion of diesel engines to natural gas, among which we can highlight Agesel SA and greenenergyperu located in Peru. The latter has been focused on the design and commercialization of machines (electric generators) and accessories therefor, which comprise a diesel generator (internal combustion engine) whose purpose is to generate energy. These two companies have used modified pistons for the reduction of the compression of the engine and mechanical mixers instead of electronic injectors for the fuel supply. In Colombia, despite the fact that the development of processes for the modification and conversion of diesel engines to natural gas has been more important today, this is an untapped market due to the current restriction of the efficient supply of natural gas throughout the country and the high costs due to the conversion (around 11 million of Colombian pesos in 2006).
Considering that the most commonly used options for converting engines are those referred to above, there is still a need for a process allowing the conversion of a diesel engine to a natural gas engine at a low cost in order to reduce pollutant emissions, without the need of an internal modification of the engine and that can be easily reversible. In this sense and in order to solve this problem, the present invention describes a process suitable for the reversible conversion of an internal combustion engine so that it efficiently operates fueled with natural gas by adding cold material in the engine head.